1. Field of the Invention
This invention generally relates to devices for carrying out the processes of countercurrent extraction, and more particularly concerns a mixer-settler for liquid-liquid extraction.
The invention can find application in the chemical, petrochemical and metallurgical fields of industry for carrying out the processes of liquid-liquid extraction.
2. Description of the Related Art
There is known a mixer-settler for liquid-liquid extraction (cf., "Handbook of Extraction", Edited by The C. Lo, Malcolm H. I. Baird, Carl Hanson, John Wiley & Sons, New York, 1983, page 280), in which each extraction chamber comprises a casing having the interior thereof divided by a vertical partition into mixing and settling zones. The vertical partition is provided with a port at the level of interface between the phases for overflow of the mixture of phases to the settling zone. The mixing zone accommodates a rotating stirrer secured to the casing, and a means for feeding the light and heavy phases. The settling zone accommodates means for removing the light and heavy phases secured to the casing.
However, a combination of the processes of stirring and transporting the phases executed by the rotating unit makes it impossible to separately effect drop size conditioning of the mixture of phases and control its volume, which results in reduced efficiency, more complicated operation of, and large production floor area occupied by this prior art apparatus.
There is also known a mixer-settler for liquid-liquid extraction (SU, A, 940, 789), in which each extraction chamber has a casing the interior of which is divided by a vertical partition into mixing and settling zones. The vertical partition has a height less than the height of the casing walls defining a gap with the base of the casing wherethrough the mixing zone communicates with the settling zone. The mixing zone accommodates a row of horizontal partitions with central holes receiving a rotatable stirring means secured to the casing, and means for feeding light and heavy fractions. These means are fashioned, respectively, as a pipe in one side wall of the casing, and a port in the other side wall of the casing. The settling zone accommodates means for evacuating the light and heavy fractions. The means for evacuating the light and heavy fractions, fashioned as a discharge weir, is made in the side wall of the casing, and has the form of a port. The means for removing the heavy phase has the form of a hydraulic seal, and is provided with a transporting means.
In this prior art extraction apparatus operations associated with mixing and conveying the phases are partially separated. The light phase flows from the settling zone to the adjacent extraction chamber by gravity, whereas the heavy phase is forcibly moved by transporting means.
The use in the known apparatus of a conventional rotatable stirrer fails to afford efficient drop size conditioning, that is to vary within a wide range the size of drops of the dispersed phase and the quantity of such drops, while at the same time ensuring a highly homogeneous composition of the mixture of phases. Another disadvantage is the lack of provision for separately conditioning the drop size in the mixture of phases in the mixing zone and its volume.
Self-overflow of the light phase between the extraction chambers, on the one hand, dictates the hydraulic dependence between the chambers, and, on the other, results in incomplete utilization of the working volume of the chambers due to the need of maintaining therein a different level, which eventually unfavourably affects controlling the composition of the mixture of phases. The aforementioned structural features of this known apparatus are not conducive to higher operation efficiency or reduced production floor area to be occupied by the apparatus.
In addition, the staggered arrangement of the mixing and settling zones in the adjacent chambers leads to expansion of the attendance area of the apparatus.